1. Field of the Invention
This invention is preferably used in information recording-reproducing apparatuses and methods employing, for example, the principle of a scanning type tunnel microscope.
2. Related Background Art
There are known various high-density recording methods, typically, magnetic recording and optical recording. In magnetic recording, the recording wavelength is determined by limitations in a device such as a magnetic head used for recording and reproduction, and in this case, the order of 1 .mu.m is the limit. In optical recording, the recording wavelength is limited by the diameter of a light beam used for recording and reproduction, and the order of 1-0.5 .mu.m is the limit.
On the other hand, in recent years, STM (scanning type tunnel microscope) has been developed and it has become possible to analyze the surface state of a solid at high resolving power, i.e., horizontal resolving power of several .ANG. and vertical resolving power of 1 .ANG. or less [G, Binning et al. Helvetica Physica Acta, 55, 726 (1982)].
Several proposals have been made to use the principle of this STM to record and reproduce variations in unevenness or electron state on the surface of a recording medium at the order of nm (U.S. Pat. No. 4,575,822, Japanese Laid-Open Patent Application No. 63-161552 and Japanese Laid-Open Patent Application No. 63-161553).
There has also been proposed a system in which an ion beam is applied to form by etching grooves for tracking and at the same time, the intensity of the ion beam is modulated in accordance with a recording signal to form depressions and form recording bits and these are reproduced by the use of the principle of STM to thereby accomplish high-density recording and reproduction of about 50 Gbits/cm.sup.2 (Japanese Laid-Open Patent Application No. 1-151035).
In such a system, however, it has been difficult to discriminate whether portions of the grooves which are free of depressions are portions which are free of recording bits or recording bits which are not depressions. Accordingly, where bits which are not depressions are continuous, it has been difficult to discriminate the number of bits.